No to the potassium sorbate, because it will inhibit yeast growth. (Use potassium sorbate as a preservative in chemically-leavened goods such as cakes, cookies... even non-leavened things such as pie crusts. Just don't use it with yeast.)
As for the calcium propionate, check my answer for details on the page to which you provided a link.
Yes, you can use ascorbic acid along with calcium propionate -- but be sure you want the effects it will have on your dough -- such as finer, softer crumb structure and shorter rise/proof times. If you're after a sturdier, more open crumb, ascorbic acid might not be for you. If you want to try it anyway, start with the bare minimum amount. I have read suggested amounts of anywhere from 15 to 80 ppm (0.0015 to 0.0080%) of the flour weight. I've had good luck with about 70 ppm (0.007 baker's percent) -- or roughly 1/16 of a teaspoon of the particular ascorbic acid per pound of flour that I have on hand. That would work out to just a shade over 1½ teaspoons per 25-pound bag of flour! I recommend weighing (especially when working with large batches that can become expensive mistakes -- and be careful; a little goes a very long way!
